Control moment gyroscopes (CMGs) are commonly employed in satellite attitude control systems. A generalized CMG may comprise a housing that supports an inner gimbal assembly (IGA). The IGA includes a rotor comprising an inertial element (e.g., a rotating ring or cylinder) coupled to a shaft. Spin bearings are disposed around the shaft ends to facilitate the rotational movement of the shaft, which may be rotated about a spin axis by a spin motor. The IGA, in turn, may be rotated about a gimbal axis by a torque module assembly (TMA) mounted to a first end of the CMG housing. To facilitate the rotational movement of the IGA, gimbal bearings are disposed between the IGA and the CMG housing. A signal module assembly (SMA) may also be mounted to a second portion of the CMG housing opposite the TMA to deliver electrical signals and power to the IGA. The CMG may also include a number of sensors (e.g., an encoder, a resolver, a tachometer, etc.) suitable for determining rotational rate and position of the IGA. Finally, a spacecraft interface (e.g., a plurality of bolt apertures) is provided on an outer surface of the CMG housing to permit the CMG to be mounted to (e.g., bolted to) a host spacecraft, such as a satellite.
To impart a desired torque to the host spacecraft, the TMA rotates the IGA, and thus the spinning rotor, about the gimbal axis. The spinning rotor is of sufficient mass and is spinning at such a rate that movement of the rotor out of its plane of rotation induces a significant torque about an output axis that is normal to the spin and gimbal axes. This torque is transmitted from the CMG rotor to the spacecraft along a rotor-to-spacecraft load path, which passes through both the IGA and CMG housings. Similarly, heat generated at the spin bearings as the result of friction may also be conducted to the spacecraft along the rotor-to-spacecraft load path.
CMGs of the type described above have been extensively engineered and are well-suited for use within spacecraft attitude control systems. This notwithstanding, conventional CMGs often provide a relatively lengthy and inefficient rotor-to-spacecraft load path. As noted above, a large portion of the rotor-to-spacecraft load path passes through the IGA and CMG housings. The IGA housing is typically thin-walled and flexible and, consequently, relatively poor at transmitting torque and conducting heat to the spacecraft. Although certain measures may be taken to stiffen the IGA housing (e.g., thickening the housing walls or providing ribs therein), these measures add surplus weight to the CMG. Furthermore, because the TMA and the SMA are mounted to opposite ends of the IGA housing, an undesirable twisting of the IGA housing and other components of the CMG is induced when the IGA is rotated about the gimbal axis.
Considering the above, it should be appreciated that it would be desirable to provide a CMG that overcomes the above-noted disadvantages. In particular, it would be advantageous if such a CMG provided an efficient rotor-to-spacecraft load path (i.e., a relatively short and stiff torque transmission path and an efficient thermal conduction path) in a relatively compact and lightweight envelope. It would also be desirable if such a CMG were designed to minimize or eliminate bending of the CMG components during gimbaling, as described above. Finally, it would be desirable if such a CMG were readily scalable. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.